On a Pixel XL, when listening podcasts, I invoke Google Assistant to initiate a call. The call goes through, but the microphone on the phone is evidently hijacked, as the remote party unable to hear me.
Another anomaly is spontaneous playback when the podcast is paused and an alert is sounded on the phone.
Check my "Audio routing issue" post http://www.doggcatcher.com/comment/17000#comment-17000 and Kenton's follow-up post http://www.doggcatcher.com/comment/17009#comment-17009